A community lives in a remote area next to a lake and they relyon the fish in the lake for food. They are concerned that the fishthey are catching from the lake have been contaminated withmercury. The lake has an area of 30,000 m2 and anaverage depth of 10 m; it is fed by a river with flow 25m3/s. Assume that 5% of the flow entering the lake islost to evaporation. Some mercury enters the water naturally fromthe soil upstream of the lake. The mercury concentration in theriver upstream is 0.07 ng/L. A small gold mining operation usesmercury or “quicksilver†to extract more metal. The runoff, whichhas a mercury concentration of 0.82 ng/L makes its way into thelake with a flow of 1 m3/s. Additionally, dry depositionof mercury from atmospheric aerosols adds mercury to the lake at arate of 12 ng/s. The lake is drained by the river flow.
- Calculate the steady-state concentration of mercury in the lake(ng/L), assuming the lake is well-mixed.
- Assume the bioaccumulation factor for mercury is 220 L/g forthe fish that the community eats. Local health officials recommendeating fish only if the mercury concentration is below 2 µg/g offish tissue. Should the community be concerned about eating thefish?
